THALLOPHYTA: ALGAE 



37 



with many pyrenoids; later there may be several chloroplasts. Reserve 

 food occurs chiefly as starch. The aerial portion may bud off new plants 

 that later become detached. When covered with water, the protoplast 

 may give rise to a number of biciliate zoospores or isogametes that escape 



E ^-^ F ^<=^ G H 



Fig. 26. Protosiphon hotryoides. A, longitudinal section of vegetative plant; B, upper 

 portion, showing scattered nuclei; C, an older stage, the cytoplasm undergoing progressive 

 cleavage; D, formation of zoospores; E and F, gametic union; G, a zygote; H, germinating 

 zygote with four nuclei. (After Bold.) 



through an apical pore (Fig. 26C-H). Gametes from the same plant may 

 pair and fuse. The zj^gote, which becomes thick-walled and dormant, 

 produces a new plant directly. If the soil becomes dry, the vegetative 

 protoplast may form aplanospores by progressive cleavage of the cyto- 

 plasm. These may be either small and uninucleate or larger and multi- 

 nucleate. The latter, upon germination, usually give rise to zoospores or 

 isogametes, but may develop into a new vegetative plant directly. 



